It's difficult to believe that the adidas Ultraboost has passed the half-decade threshold. Naturally, the credit for revolutionizing running footwear is well deserved, but in running, and in technology, you can't move ahead if you're standing still or looking backwards. 

The Ultraboost 21 offers the most advanced combination of Boost, Torsion and Primeknit to date. A 6% increase in the amount of Boost maximizes the bouncy energy returning cushioning, while an updated Torsion system offers a 15% increase in forefoot bending stiffness, for greater responsiveness. The upper is upgraded as well, with the Primeknit textile making use of the recycled Parley Ocean Plastic recycled material incorporating Primeblue.

If a size is not listed, it is sold out. 

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